1. Field of the Invention
The present invention relates to a rewritable optical disc, and a recording method and a reproduction method for the optical disc. The present invention in particular relates to an optical disc recording apparatus and an optical disc recording method which each record video objects (compressed audio and video data) so that the seamless reproduction of the video objects is possible even if a pause operation was designated by a user during recording, and an optical disc apparatus for the optical disc recording apparatus and the optical disc recording method.
2. Background Art
In recent years, optical discs with a capacity of several gigabytes, such as DVD-RAMs (digital video disc-random access memories), have appeared in the field of rewritable optical discs that had formerly been limited to a capacity of 650 MB.
It is expected that such optical discs will become the principal media for recording AV (audio-visual) data as well as computer data. That is, it is believed that optical discs and recording and reproduction apparatuses for the optical discs (hereinafter abbreviated to the “optical disc apparatuses”) will replace magnetic tapes and VCRs (videocassette recorders) that have conventionally been the major AV data recording media and AV data recording apparatuses.
The operation of an optical disc apparatus used instead of a stationary VCR is described below. The optical disc apparatus receives television signals of a broadcast, converts the signals into a video object, and records the video object onto an optical disc. More specifically, the optical disc apparatus generates compressed video data (a video elementary stream) and compressed audio data (an audio elementary stream) from the television signals, divides the compressed video data into video packs of a fixed length, and divides the compressed audio data into audio packs of a fixed length. Then the optical disc apparatus interleaves the video packs and audio packs and records the interleaved packs onto optical discs as a video object. Here, the video elementary stream and the audio elementary stream are generated according to an MPEG standard (ISO/IEC13818).
The optical disc apparatus usually generates one video object in each recording operation if a pause operation (the temporary halt of recording) is not designated during the recording operation. That is, if no pause operation is designated during recording, the optical disc apparatus generates and records one video object for the period between the time when a user designates the start of recording and the time when the user designates the end of recording.
If a pause operation is designated during recording, a problem arises in the optical disc apparatus. That is, it becomes difficult for the optical disc apparatus to seamlessly reproduce video objects generated before and after a pause operation.
If one video object is generated by each successive recording operation, the optical disc apparatus completes the generation and recording of a current video object on receiving a pause designation and starts to generate and record a new video object on receiving a pause release designation. That is, one video object is generated and recorded for each of the period between a designation of recording start and a pause designation, the period between a pause release designation and the next pause designation, and the period between a pause release designation and a designation of recording end.
If a video object recorded until a pause designation and a video object recorded after a pause release designation are sequentially reproduced, the optical disc apparatus cannot guarantee the seamless reproduction of these video objects and the following problems may occur.
To prevent overflows and underflows of video elementary streams in the video input buffer of a reproduction apparatus, the optical disc apparatus assumes the video input buffer and carries out a simulation to determine the size of data accumulated in the video input buffer during the encoding of video data. Similarly, during the encoding of audio data, the optical disc apparatus assumes an audio input buffer and carries out a simulation to determine the size of data accumulated in the audio input buffer. Although this guarantees that each video object can be seamlessly reproduced by itself, an overflow and underflow may occur in the reproduction apparatus at the boundary between a video object recorded until a pause designation and that recorded after a pause release designation.
Also, each audio elementary stream includes a plurality of audio frames (each audio frame is of 32 ms, for instance). If separate video objects are generated as a result of a pause operation, noise (electric noise) may occur at the boundary between these video objects because the audio frame at the boundary includes audio data having no correlation.